Asphalt roofing shingles are manufactured by taking a continuous base sheet of organic felt or fibreglass, saturating it in a base asphalt, covering it with a coating asphalt, and then embedding granules on the top side of the coated sheet. The granules protect the asphalt from breaking down through oxidization by ultra violet rays. The finished sheet is cut into lanes and to a desired length of shingles.
The granules are applied with a pattern of colored blends that repeat over several shingles. This pattern allows for a colorful and decorative capping for the house yet ideally prevents any undesired repetitive patterns from forming on the roof once the shingles are installed. In some cases, it is desired to provide additional decoration by providing a second layer of asphalt coating to portions of the exposed parts of the shingle and then embedding granules in these patches of fresh asphalt. These patches of asphalt and granules allow for two contrasting colors on top of each other to add to the variety of the shingle appearance.
In the past, the patches of contrasting color granules have often been applied in a regular pattern which is the same on each shingle. A difficulty with this is that when the shingles are installed, the resultant pattern is repetitious or uniform and may not be sufficiently attractive.
U.S. Pat. No. 4,352,837 issued Oct. 5, 1982 to Certain-Teed Corporation suggests a way of dealing with this problem. In the Certain-Teed patent, a series of spaced apart bands or patches of granules are applied as a second layer to the first uniform layer of granules, the patches of the second layer having various widths and being applied with a periodicity different from the shingle length. This results in a random appearance since the same pattern does not repeat on any two shingles for a relatively large number of shingles.
When the random method described above is used for applying a second layer of asphalt and granule patches, the roofer can experience difficulty while applying capping and ridges. When a roofer applies capping and ridges, he usually cuts the shingles into thirds (called tabs) and bends the tabs over the peak. If a patch, ie. a second layer of asphalt and granules, is on the apex of the ridge, it will tend to crack as the tab is bent over the ridge. Therefore, preferably the roofer should have a series of shingles available which do not have patches at the centers of the tabs. However, when the pattern of patches is relatively random, the roofer will not usually be able to find sufficient such shingles, at least not without a great deal of looking.
It is therefore an object of the invention to provide a method of making shingles which achieves a variable arrangement of pattern and yet which at the same time also provides groups of shingles which are identical. Thus a roofer can use such shingles to produce a roof which will have a pleasing appearance, and yet it is possible, using such a method, to produce shingles where at least one or two thirds of such shingle (ie. one or two tabs) do not have patches (ie. second layers of asphalt and granules) at their centers. This will permit less waste and allows the roofer to help ensure that caps and ridges are properly installed.